Electromagnetic wheel brake device

ABSTRACT

An electromechanical wheel brake device for a motor vehicle, having an electric motor for driving two planetary gears, connected in series with one another, which actuate the wheel brake device via a threaded roller gear. The planetary gear is provided with a first electromagnetic coupling, with which a sun wheel of the second planetary gear can be locked, or can be connected in a manner fixed against relative rotation to a sun wheel of the first planetary gear, and with a second electromagnetic coupling, with which a ring gear of the second planetary gear can be stopped or can be connected in a manner fixed against relative rotation to a ring gear of the first planetary gear. By means of the electric motor, by switching of the two couplings, the rolling thread drive can be driven fast to overcome an air gap, slowly and with major speed reduction for the ensuing exertion of a high braking force, and fast for releasing without a reversal of the direction of rotation of the electric motor. For use as a parking brake, both couplings are switched to be without current, as a result of which the second planetary gear is blocked and an imposed braking force is maintained while the electric motor is stopped.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 99/02199 filed onJul. 15, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electromechanical wheel brake device whichis intended in particular for use in a motor vehicle.

2. Description of the Prior Art

One electromechanical wheel brake device is known from German PatentDisclosure DE 38 40 685 A1. This known wheel brake device has anelectric motor and three series-connected planetary gears, the first ofwhich can be driven by the electric motor. The third planetary gearactuates a brake actuating device of the wheel brake device, and thebrake actuating device of the known wheel brake device has a double camthat is rotatable with the third planetary gear and that presses twobrake jaws (friction brake linings) against a brake drum (brake body) ofthe wheel brake device, embodied as a drum brake. One of the planetarygears, preferably the first one, has two switchable couplings, withwhich, selectively, a ring gear of the planetary gear can be locked or aring gear of the planetary gear can be connected to the ring gear in amanner fixed against relative rotation. In the case of the ring gearrotationally fixed to the ring gear, one planetary gear is bridged; itsgear ratio is 1:1. In this state, only the two outer planetary gearseffect a speed reduction, and as a result the brake actuating device isactuable fast, but with low moment or low force. In this state, an airgap between the friction brake linings and the brake body is overcome.After reversing the two couplings, the planetary gear equipped with thecouplings executes a speed reduction as well; the overall result is agreater speed reduction over all three planetary gears. In this state,the brake actuating device is indeed actuated more slowly, but withgreater force or greater moment. This situation serves to press thefriction brake linings, already contacting the brake body, against thebrake body with great force and as a result to attain a high brake forceand a high braking moment.

SUMMARY OF THE INVENTION

The wheel brake device of the invention has two planetary gears and twoswitchable couplings. One of the two switchable couplings, in oneswitching position, stops a sun wheel of the second planetary gear, andin another switching position, it connects the sun wheels of the twoplanetary gears to one another in a manner fixed against relativerotation. The second coupling, in one switching position, stops a ringgear of the second planetary gear, while in another switching positionit connects the ring gears of the two planetary gears to one another ina manner fixed against relative rotation. The wheel brake device of theinvention makes four switching states of its two planetary gearspossible, namely a fast gear and a slow gear for tightening the wheelbrake device, a fast gear with a reversal of the direction of rotationfor releasing the wheel brake device, and a locked position, in whichthe two planetary gears cannot retate, so that a braking force exertedis also maintained while the electric motor is without current.

The wheel brake device of the invention has the advantage that an airgap between the friction brake lining and the brake body is rapidlyovercome with it, and then, by a transition to a higher gear ratio, ahigh contact pressure of the friction brake lning against the brake bodycan be attained. Another advantage is that with the same direction ofrotation of the electric motor, the contact pressure of the frictionbrake lining against the brake body can be reduced, and the wheel brakedevice can be released entirely; accordingly, upon release of the wheelbrake device the electric motor is operated in the same direction ofrotation as in tightening of the brakes. Hence no reversal of thedirection of rotation and no reversing mode of the electric motor arenecessary. When operating the wheel brake device, the electric motor ismerely turned on and off, and a pwer switches suffices for this purpose.Conversely, to reverse the direction of rotation and no reversing modeof the electric motor are necessary. When operating the wheel brakedevice, the electric motor is merely turned on and off, and a powerswitch suffices for this purpose. Conversely, to reverse the directionof rotation would require a full bridge with four power switches.Another advantage of the invention is that the restoration of the wheelbrake device takes place at high speed, so that the wheel brake devicetakes place at high speed, so that the wheel brake device is releasedrapidly. In addition, the wheel brake device of the invention has theadvantage of improved dynamics, since in a rapid alternation oftightening and releasing, or from increasing the contact pressure of thefriction brake lining against the brake body to reducing the contactpressure and vice versa, the direction of rotation of the electric motoris not reversed counter to its moment of inertia, but rather ismaintained unchanged, so that in a rapid alternation, the moment ofinertia of the electric motor can even be utilized. This makes the wheelbrake device of the invention especially well suited to anti-lock,traction control and/or electronic stability control, which necessitatea rapid alternation between tightening and release, or betweenincreasing and reducing the braking force.

Preferably, the two switchable couplings are embodied as electromagneticcouplings, which in a basic position without current, stop the sun wheeland the ring gear of the second planetary gear. In this way, the wheelbrake device is stopped, so that an imposed contact pressure of thefriction brake lining against the brake body is maintained, even whenthe electric motor has no current. As a result, the wheel brake devicecan be used as a parking brake.

For converting the rotary motion of the second planetary gear into atranslational motion for pressing the friction brake lining against thebrake body, in one feature of the invention the actuating device of thewheel brake device has a screw thread, which is preferably embodied as athreaded roller gear for the sake of improved efficiency and lowfriction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail below, with referenceto the drawing in which the sole drawing FIGURE shows an exemplaryembodiment of a wheel brake device of the invention in section, in apartly simplified, schematic illustration.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The electromechanical wheel brake device of the invention, identifiedoverall by reference numeral 10, is embodied as a disk brake having abrake caliper 12, to which a gearbox 14 is flanged. Two series-connectedplanetary gears 16, 18 are received in the gearbox 14. Each planetarygear 16, 18 has one sun wheel 20, 22, three planet wheels 24, 26, andone ring gear 28, 30. Only one of the planet wheels 24, 26 can be seen,since the other two planet wheels are located in front of and behind theplane of the drawing, and the planet wheel located behind the plane ofthe drawing is concealed by the respective sun wheel 20, 22.

The sun wheel 20 of the first planetary gear is seated in a manner fixedagainst relative rotation on a motor shaft 32 of an electric motor 34,which is flanged from outside to an end wall 36 of the gearbox 14. Acylindrical pole body 38 of a first, switchable electromagnetic couplingis mounted in a manner fixed against relative rotation on a face end,which is remote from the electric motor 34 and oriented toward thesecond planetary gear 18, of the sun wheel 20 of the first planetarygear 16.

The planet wheels 24 of the first planetary gear 16 are supportedrotatably on axle pins 42, which are anchored firmly in the end wall 36of the gearbox 14. The planet wheels 24 of the planetary gear 16 arethus received in stationary fashion, but rotatable about their own axes,in the gearbox 14, while the end wall 36 of the gearbox 14 forms astationary planet carrier of the first planetary gear 16.

The ring gear 28 of the first planetary gear 16 has a laterallydisposed, hollow annular collar 44, in which a coil 46 is received. Theannular collar 44 is located on a side of the ring gear 28 orientedtoward the second planetary gear 18. It forms a pole body 44 of asecond, switchable electromagnetic coupling and is closed, on the sidetoward the second planetary gear 18, by a friction lining 48 that is acomponent part of the second coupling.

An annular, disk-like brake ring 50 is riveted to the axle pins 42 ofthe planet wheels 24 of the first planetary gear 16. The brake ring 50is located in an interstice between the first and second planetary gears16, 18. Since the axle pins 42 are firmly anchored in the gearbox 14,the brake ring 50, riveted to the axle pins 42, is also retained instationary fashion in the gearbox housing 14.

The brake ring 50 cooperates with armature plates 52, 54 of the twoelectromagnetic couplings 38, 40, 52; 44, 46, 48, 54. The armatureplates 52, 54 are disposed in the same plane, in an interstice betweenthe brake ring 50 and the first planetary gear 16. The armature plate 52of the first electromagnetic coupling 38, 40, 52 has the shape of acircular disk and is encircled by the armature plate 54, having the formof an annular disk, of the second electromagnetic coupling 44, 46, 48,54.

The armature plate 52 of the first electromagnetic coupling 38, 40, 52is riveted to an outer rim of a cup spring 56, whose inner rim isriveted to the sun wheel 22 of the second planetary gear 18. Via the cupspring 56, the armature 52 of the first electromagnetic coupling 38, 40,52 is connected in a manner fixed against relative rotation to the sunwheel 22 of the second planetary gear 18. The cup spring 56 attracts thearmature plate 52 in the direction of the sun wheel 22; that is, thearmature plate 52 rests on the brake ring 50, connected in a mannerfixed against relative rotation, in the gearbox 14 because of the springforce of the cup spring 56. In this currentless basic position of thefirst electromagnetic coupling 38, 40, 52, the sun wheel 22 of thesecond planetary gear 18 is locked against rotating.

By supplying electric current to the coil 40 of the firstelectromagnetic coupling 38, 40, 52, the armature place 52 is raisedfrom the brake ring 50 counter to the spring force of the plate spring56 and is brought into frictional engagement with the pole body 38 ofthe first electromagnetic coupling 38, 40, 52. In this switchingposition attained with current of the first electromagnetic coupling 38,40, 52, the sun wheel 22 of the second planetary gear 18 is connected ina manner fixed against relative rotation, via the cup spring 56, to thesun wheel 20 of the first planetary gear 18.

The armature disk 54 of the second electromagnetic coupling 44, 46, 48,54 is riveted to an outer edge of an annular cup spring 58, whose innerwall is joined to the ring gear 30 of the second planetary gear 18. As aresult, the armature plate 54 of the second electromagnetic coupling 44,46, 48, 54 into contact with the brake ring 50 fixed in a gearbox 14, sothat in the currentless basic poition of the second electromagneticcoupling 44, 46, 48, 54, the ring gear 30 of the second planetary gear18 is retained non-rotatably in the gearbox 14. By supplying current tothe coil 46, the second electromagnetic coupling 44, 46, 48, 54 isswitched over to its switching position with current, in which itsarmature plate 54 is lifted by magnetic force, counter to the springforce of the annular cup spring 58, from the brake ring 50 and pressesin frictional engagement against the friction brake lining 48 of thesecond electromagnetic coupling 44, 46, 48, 54. In this switchingposition with current of the second electromagnetic coupling, 44, 46,48, 54, the ring gears 28, 30 of the two planetary gears 16, 18 areconnected to one another in a manner fixed against relative rotation.

The planet wheels 26 of the second planetary gear 18 are supported,rotatable about their own axes, on a planet carrier 60, which in turn issupported rotatably on the brake caliper 12 by means of a ball bearing62. The planet wheels 26 of the second planetary gear 18 can accordinglyrevolve about the sun wheel 22, in the conventional way for planetarygears, and can also rotate about their own axes.

The sun wheel 22 of the second planetary gear 18 is rotatably supportedon a shaft stub 64, which is integral with the planet carrier 60.

For converting a rotary motion of the planet carrier 60 into atranslational motion for pressing two friction brake linings 66 againsta brake disk 68, the wheel brake device 10 has a brake actuating device70. The brake actuating device 70 is embodied as a threaded roller gearand is accommodated in a bore 72, which is made perpendicular to thebrake disk 68 and coaxial to the planetary gears 16, 18 in the brakecaliper 12. The threaded roller gear has a spindle 74, which is bracedin the bore 72 of the brake caliper 12 via an axial roller bearing 76.Via a square peg 78, which is integral with the planet carrier 60 of thesecond planetary gear 18 and which engages a complimentary square hole80 in the spindle 74, the spindle 74 is connected by positive engagementto the planet carrier 60 in a manner fixed against relative rotation.The spindle 74 is gripped by a nut 82, which is coaxial with the spindle74 and has a greater thread diameter than the spindle 74, creating anannular interstice between the spindle 74 and the nut 82. A number ofthreaded rollers 84 are disposed in the interstice, and these rollersmesh with both the thread of the spindle 74 and the thread of the nut82. The spindle 74, nut 82 and threaded rollers 84 are component partsof the threaded roller gear.

By driving the spindle 74 to rotate, the threaded rollers 84 are drivento a revolving motion, complementary to that of the planet wheels of aplanetary gear, around the spindle 74, while at the same time thethreaded rollers 84 rotate about their own axes. Because of the slopesof the threads of the spindle 74, nut 82, and threaded rollers 84, therevolving motion of the threaded rollers 84 and the rotation about theirown axes causes an axial displacement of the nut 82. The displacement ofthe nut 82 takes place even whenever the threaded rollers 84, as in theexemplary embodiment shown, have a thread pitch of zero, or in otherwords are provided with revolving grooves instead of a thread. By meansof its displacement, the nut 82 presses the friction brake lining 66,mounted on it, against one side of the brake disk 68. The other frictionbrake lining 66 is pressed in a manner known per se, by reaction force,against the other side of the brake disk 68 via the brake caliper 12embodied as a floating caliper.

The function of the wheel brake device 10 of the invention is asfollows: For overcoming an air gap between the friction brake linings 66and the brake disk 68, the first coupling 38, 40, 52 is supplied withcurrent, as a result of which its armature disk 52 is lifted from thefixed brake ring 50 in the gearbox 14 and is brought into frictionalengagement with the pole body 38 of the first electromagnetic coupling38, 40, 52. The sun wheel 22 of the second planetary gear 18 isconnected in a manner fixed against relative rotation to the sun wheel20 of the first planetary gear 16 and thus in a manner fixed againstrelative rotation to the motor shaft 32. By supplying current to theelectric motor 34, the sun wheel 22 of the second planetary gear 18 isdriven by the electric motor 34 to rotate directly, and via the planetwheels 26 and the planet carrier 60 of the second planetary gear 18, itdrives the spindle 74 of the threaded roller gear 74, 82, 84 to rotate.The ring gear 30 is retained non-rotatably in the gearbox 14 by thesecond, currentless coupling 44, 46, 48, 54. The nust 82 displaces thefriction brake lining 66 mounted on it directly, and displaces theopposite friction brake lining 66 indirectly via the brake caliper 12into contact against the brake disk 68. When the air gap between thefriction brake linings 66 and the brake disk 68 is overcome, the ringgear 28 or the first planetary gear 16 is a freely rotatable, while tahefirst planetary gear 16 is out of operation.

As soon as the friction brake linings 66 rest on the brake disk 68, thecontact pressure of the friction brake linings 66 against the brake disk68 that is required to generate a braking force or braking moment, andconsequently the requisite driving torque of the threaded spindle 74,rise abruptly. This can easily be ascertained, for instance from anabrupt increase in the current consumption of the electric motor 34 orfrom the drop in its rpm. To apply the requisite contact pressure forbraking when the friction brake linings 66 are contacting the brake disk68, current is supplied not only to the first coupling 38, 40, 52 butalso to the second coupling 44, 46, 48, 54. Thus, in addition to the sunwheels 20, 22, the ring gears 28, 30 of the two planetary gears 16, 18are also connected to one another in a manner fixed against relativerotation. While the sun wheel 22 of the second planetary gear 18,connected to the motor shaft 32 ina manner fixed against relativerotation, rotates at the same speed as the motor shaft 32, the ring gear30 of the second planetary gear 18 is driven to a rotary motion in theopposite direction from the sun wheel 22 of the second planetary gear18, via the sun wheel 20, the planet wheels 24 that are rotatable aboutthe stationary axle pins 42, and the ring gear 28 of the first planetarygear, with which the ring gear 30 of the second planetary gear 18 isconnected in a manner fixed against relative rotation via the secondcoupling 44, 46, 48, 54, which has current. The second planetary gear 18in this state acts as a differential gear; the rotation of the sun wheel22 and the ring gear 30 are superimposed on one another, and the speedof revolution of the planet wheels 26 of the second planetary gear 18 isreduced considerably, and thus the torque transmitted by the electricmotor 34 to the spindle 74 of the threaded roller gear 74, 82, 84 isincreased by a multiple of the original value. Since the sun wheels 20,22 of the two planetary gears 16, 18 have the same diameter, and theplanet wheels 24 of the first planetary gear 16 are larger than theplanet wheels 26 of the second planetary gear 18, the planet wheels 26of the second planetary gear 18 continue to revolve in the samedirection as when the air gap between the friction brake linings 66 andthe brake disk 68 is overcome.

To reduce the brake force, release the wheel brake device 10, and adjustthe air gap between the friction brake linings 66 and the brake disk 68,the first coupling 38, 40, 52 is not supplied with current, while thesecond coupling 44, 46, 48, 54 is supplied with current; the electricmotor 34 is supplied with current, specifically with the same polarityas when the wheel brake device 10 is tightened; that is, in tighteningand in releasing the wheel brake device 10, the electric motor 34 hasthe same direction of rotation. The first coupling 38, 40, 52, which iscurrentless, keeps the sun wheel 22 of the second planetary gear 18non-rotatable. The spindle 74 is driven to rotate via the sun wheel 20,the planet wheels 24, and the ring gear 28 of the first planetary gear16, the ring gear 30 of the second planetary gear 18, which rotates withthe ring gear 28 of the first planetary gear 16, and the planet wheels26 of the second planetary gear 18, which revolve about the stopped sunwheel 22 of the second planetary gear 18. The two planetary gears 16, 18effect a reversal of the direction of rotation; for the same directionof rotation of the motor shaft 32, the spindle 74 rotates in theopposite direction from before, so that the friction brake linings 66are lifted from the brake disk 68.

For the sake of maintaining an imposed brake force, the two couplings38, 40, 52; 44, 46, 48, 54 are not supplied with current; they stop thesun wheel 22 and the ring gear 30 of the second planetary gear 18, as aresult of which the second planetary gear 18 is blocked, so that thespindle 74 of the threaded roller gear 74, 82, 84 does not rotate, evenwhen the electric motor 34 is currentless. An imposed brake force ismaintained. The brake device 10 of the invention can accordingly be usedas a parking brake. A braking force during a braking event can also bekept constant, without having to supply current to the electric motor34, which has the advantage of saving energy and of producing lessheating of the electric motor 34.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. An electromechanical wheel brake device for amotor vehicle comprising an electric motor (34) a first planetary gear(16) driven by said electric motor, a second planetary gear (18) whichis driven by said first planetary gear, a brake actuating device whichis actuated by said second planetary gear and with which a frictionbrake lining can be pressed against a brake body and raised again, thebrake body being rotationally fixed to a vehicle wheel, said first andsecond planetary gears (16, 18) having different gear ratios, a firstswitchable coupling (38, 40, 52), which in one switchable position stopsa sun wheel (22) of said second planetary gear (18) and in anotherswitchable position connects the sun wheels (20, 22) of said first andsecond planetary gears (16, 18) to one another in a manner fixed againstrelative rotation, and a second, switchable coupling (44, 46, 48, 54),which in one switchable position stops a ring gear (30) of the secondplanetary gear (18) and in another switchable position connects the ringgears (28, 30) of the two planetary gears (16, 18) to one another in amanner fixed against relative motion, wherein a planet carrier (60) ofsaid second planetary gear (18) actuates a brake actuating device (70).2. The electromechanical wheel brake device of claim 1, wherein saidfirst planetary gear (16) has a higher gear ratio than said secondplanetary gear (18).
 3. The electromechanical wheel brake device ofclaim 1, wherein the planet carrier end wall (36) of said firstplanetary gear (16) is stationary.
 4. The electromechanical wheel brakedevice of claim 1, wherein at least one of said first and secondswitchable couplings (38, 40, 52; 44, 46, 48, 54) is embodied as anelectromagnetic coupling.
 5. The electromechanical wheel brake device ofclaim 4, wherein both said switchable couplings (38, 40, 52; 44, 46, 48,54) are embodied as electromagnetic couplings, and wherein, in a basicposition without current, said first switchable coupling (38, 40, 52)stops the sun wheel (22), and said second switchable coupling (44, 46,48, 54), in a basic position without current, stops the ring gear (30)of said second planetary gear (18).
 6. The electromechanical wheel brakedevice of claim 1, wherein said brake actuating device (70) has a screwthread comprising a threaded roller gear (74, 82, 84).